The present invention relates to a gripping device and more particularly relates to a gripping device or other manipulating device of the type which is pivotally suspended from a crane and which is operated hydraulically or pneumatically by way of a pressure medium. In particular the invention relates to a gripping device which is operated by means of a double-acting hydraulic or pneumatic cylinder movement of a piston within the cylinder controlling two gripping claws which co-operate to form the gripping device. The gripping claws are pivotally mounted on or adjacent the hydraulic cylinder and the entire assembly of the gripping claws and the hydraulic cylinder is connected to a crane by way of a universal joint which permits pivotal movement on one or more axes.
The development of the hydraulic telescopic and/or folding arm crane has proved most useful in connection with the rapid and rational manipulation of various types of goods, and has thus contributed to making various transportation and supply operations more efficient. In order to minimise the strain and other stresses applied to he crane the gripping means is usually pivotally suspended from the crane or flexibly suspended. Often the joint member permits pivoting movement in all directions and is thus truly a universal joint, and in such gripping devices two or more joints may be provided having joint hinges permitting pivotal movement about axes that are at an angle to each other. In certain cases this flexible mounting of the gripping member is a advantage, for example where the reach of the device is to be extended. However, in certain cases the flexibility is a disadvantage in that it may be difficult to control the precise movements of the gripping claws and consequently it is desirable to provide a gripping device in which it is possible instantaneously to stiffen the pivotal connecting joints in order to obtain better control of the gripping claws.